Migrating from ADG1606 to ADG726

Thanks in advance for your help. My team is currently using two analog multiplexer ADG1606 chips to control 31 signal channels. The PCB power is +/-5v. Due to some new design specifications, we will now power the PCB with a single 5v supply and therefore have decided to migrate to ADG726 or something similar. This time, we are looking for 65 channels total. After looking through the datasheet for ADG726, I have some questions:

1) We have a 2.5v reference from our ADC/DAC chip, but overall PCB ground must remain at 0v. Which voltage should we choose for GND on this chip?

2) It looks like pins 13 and 14 are both VDD. What is the reason for that?

3) We want to reduce leakage current as much as possible. Are we better off selecting 726 over 732? If there is no difference in performance then 732 may be simpler.

4) Since we need 65 channels overall, I wonder if there is a single switch with the same characteristics (especially parasitic capacitance)? Maybe there is a whole family of chips that behave the same as this one.

The GND for the chip should be at 0V; the signal voltage should not go below the chip GND.

Both pins are used to supply the switching components and digital supply; VDD should be supplied to both pins.

The drain off-leakage on the ADG726 is twice the ADG732 because there are twice as many switches connected to each drain. If you connected the two drain pins, DA and DB, the off leakage will be the same for both models.

Capacitance is a factor of the switch size and the configuration; a single switch will have much smaller drain capacitance than a 16:1 multiplexer, and typically, they are designed to decrease capacitance. Therefore we do not have single switch that will match the ADG726. The closest I can find would be either the ADG801 or ADG601.

The GND for the chip should be at 0V; the signal voltage should not go below the chip GND.

Both pins are used to supply the switching components and digital supply; VDD should be supplied to both pins.

The drain off-leakage on the ADG726 is twice the ADG732 because there are twice as many switches connected to each drain. If you connected the two drain pins, DA and DB, the off leakage will be the same for both models.

Capacitance is a factor of the switch size and the configuration; a single switch will have much smaller drain capacitance than a 16:1 multiplexer, and typically, they are designed to decrease capacitance. Therefore we do not have single switch that will match the ADG726. The closest I can find would be either the ADG801 or ADG601.

Thanks Sean! These answers are very helpful. I just want to make sure I understand #1 better... I think we should look at the figure for Test Circuit 4. For us, the VD (and VS) voltage will be an AC signal centered at DC 2.5v. In your answer, you say that the signal should not go below chip GND. If I imagine setting GND to DC 2.5v, then we would clip the negative half of the AC signal?

The part that confuses me is how to configure as +/-2.5v if that is the case. Maybe I am missing something... but that is exactly why I'm asking!

You indicate that you have a 2.5V reference; I assume that means your AC signal is centred on 2.5V, i.e. your signal goes from 0V to 5V.

If this is the case, then the ADG726 should be powered by VSS = GND = 0V and VDD = 5V.

If you place the ADG726 GND = 2.5V, VSS = 0V and VDD = 5V, that is the equivalent of a ±2.5V Dual supply. However, you will have to translate your digital signals so that they are referenced to the 2.5V as GND, i.e.VINH = 2.5+1.7 = 4.2V and VINL = 2.5 + 0.7 = 3.2V.

The switch characteristics will be the same as long as there is a 5V difference between VDD and VSS.